1. Technical Field
The present invention relates to image processing for a projector, and in particular to a distortion correction technology of an image displayed on a projection screen.
2. Related Art
There are used projectors adapted to project an image on a screen based on image data using an optical system, which is composed of various optical elements such as light valves, digital mirror devices, and a dichroic prism, and illumination light from a light source. Although the screen for the projectors is formed to have a planar shape, the shape is not a perfect plane, but has a slight bulge with a wrinkle or a slack caused by an installation environment, the temperature, the material of the screen, and aged deterioration. In particular in a portable take-up screen, when carrying or retracting the screen, the pipe for retracting the screen is apt to creep to cause the wrinkle and the slack.
It is known that when projecting an image on the screen with the wrinkle or the slack is caused thereon, a distortion is caused in the image by the bulge derived from the wrinkle or the slack. As a technology for eliminating the distortion in the image, there is disclosed a technology of, for example, projecting a pattern image having dot figures, which are arranged in the same intervals in both of the horizontal and vertical directions of the screen, on the screen, and then executing a distortion correction on the image based on the positional difference between the position on the screen where the dot figures are displayed and the position in the original pattern image where the dot figures are displayed, thereby projecting an image without distortion on the screen.
JP-A-2001-083949 and JP-A-2004-228619 are examples of a related art document.
However, the amount of distortion of the image displayed by the projection light entering the same position varies in accordance with the incident conditions such as the incident direction, the incident angle, and so on of the projection light to the screen. Therefore, in the case in which the pattern image with the dot figures arranged at the same intervals is used as in the related art, it is not achievable to detect the variation in the amount of distortion in accordance with the difference in the incident conditions of the projection light with high accuracy, and therefore, there is caused a problem that it is not achievable to correct the distortion of the image projected on the screen with high accuracy. Further, in the case in which the pattern image having dot figures arranged thickly at the same intervals is used, the amount of distortion must be calculated as many times as the number of characteristic points, which increases the processing load of the projector, and incurs increase in the processing time.